Ok, I'll try my hand at this.
1) If she has fun with him.
2) If she is entertained by him.
Well, neither of these are my job. I am not an entertainer or a comedian. Yes, I can make women laugh, but it has to be a mutual thing. If you can't hold up your end of a conversation, funny or otherwise, you'll never get far in the world of interpersonal relationships.
3) If she feels safe with him.
4) If she thinks she has something to gain by being with him.
In some ways, #3 is a subordinate of #4, i.e. a woman can gain safety by being with a man. IMHO, most women like a man who is a little dangerous. After all, if a woman wanted a sure-fire emotional safety net, she'd date another woman. If they are looking for physical safety, then a pistol is a better bet than a lot of the guys walking around in this day and age.
5) If her mind is stimulated by him.
Now we are getting to the meat of the issue. Women are like cats. Curious, always testing you and delicious when properly cooked. But I digress. Young women like a challenge, especially a guy who doesn't get along with his Dad. An example:
Guy #1 says: "My Dad is a my role model, and we get along great. I want to go to college and graduate business school and my Dad supports this idea 100%."
Guy #2 says: "My old man is an a$$hole. I want to be a rock star but he keeps telling me to cut my hair and get a job."
Yep, you guessed it, women will want to clasp guy #2 to their bosom and comfort him, 'cause he's a misunderstood rebel. Guy #1 will be the woman's friend, you know, the friend who puts new brakes on her car for her (for free) and gives her a place to stay (for free) when guy #2 throws her out in the street after an argument.
You see, guy #1 is inherently self-sufficient and anyway has his parent(s) to fall back on. He is typically not emotionally needy. He has clear, attainable goals in life and typically is not generating the type of emotional/dramatic challenges that young women like.
Guy #1 is the "friend in need" of women everywhere, the 'McGyver' whom they turn to when the chips are down. Of course, being a gentleman, he will not cash in on his female friends during their hour of need by trying to score on them when they just broke up with their rockstar boyfriend, for the third time in a month, now that they need a place to stay yet again.
6) If she is sexually attracted to him.
Well, this one is easy. This is why some chick picks you up/gets picked up in a bar. Sometimes it's biology, not psychology. Here is where the great ass, nice car and ability to hold your liquor really pays off.